The present invention relates to connectors for connecting ends of optical fibers together. The invention relates more particularly to fiber optic cable connectors for cables in the form of ribbons and to tools for installing the connectors on the ends of the cables.
Fiber optic ribbon cable generally comprises a plurality of optical fibers arranged parallel to one another in a side-by-side planar array and bound together by a matrix covering of polymer material. Ribbon cables are typically terminated by a single connector that is attached to the end of the cable, since it is more cost-effective to employ a single connector for the multiple fibers of the cable than to use a separate connector for each fiber.
A variety of connectors and connection methods have been proposed for terminating fiber optic ribbon cables. One approach that has been taken is to mechanically bind the fibers to the connector using a heat-activated epoxy adhesive. Unfortunately, this technique requires time and a heat source to cure the adhesive. Furthermore, after curing of the adhesive, the ends of the ribbon fibers then must be polished to restore their optical performance. The polishing equipment is expensive, and the process is time-consuming and not practical for use in the field.
U.S. Pat. No. 5,093,881 discloses a ribbon cable connector having a ferrule formed by two semi-cylindrical elements defining opposing faces between which the fibers of a cable are disposed, and a sleeve that surrounds the ferrule. One of the semi-cylindrical elements of the ferrule defines a plurality of V-shaped grooves formed in its face that opposes the other semi-cylindrical element and extending over part of the element""s length. The grooves receive end portions of the fibers that have been stripped of the plastic covering of the ribbon cable, with the end faces of the fibers flush with an end face of the ferrule. The remainder of the length of the element has a recess defined in the face for receiving a length of the ribbon cable having the plastic covering still intact. The ribbon cable is secured in the ferrule by an adhesive applied in the recess containing the non-stripped part of the cable. Installing the connector of the ""881 patent requires polishing or lapping the end face of the ferrule and the end faces of the fibers after the fibers are secured in the ferrule. Thus, the connector is not convenient for use in the field.
U.S. Pat. No. 4,142,776 discloses a two-piece connector for fiber optic ribbon cable, having a substrate with fiber-receiving grooves and a mating cover placed in facewise opposition to the substrate covering the fibers in the grooves. The connector is contained in a cartridge, either with an interference fit that forces the cover and substrate together to clamp the fibers therebetween, or with a clearance between the cartridge and the connector in which case set screws are used for providing the clamping force urging the cover and substrate together. A similar two-piece connector on the end of another cable is also disposed in the cartridge with end faces of the connectors in abutting relation. The ""776 patent indicates that polishing of the end faces of the fibers and connector is optional, but if polishing is to be accomplished with the connector of the ""776 patent it must be performed after the fibers are installed in the connector. Thus, the connector is not practical for use in the field.
U.S. Pat. No. 4,964,688 discloses a fiber optic connector and method for its use, in which a fiber optic stub is secured in a passage extending through a connector body with a first end face of the stub flush with a first end face of the connector body and an opposite second end face of the stub in the passage. An optical fiber is inserted into the passage from the opposite second end of the connector body until the end of the fiber abuts the second end face of the stub. The optical fiber is adhesively secured in the connector body. The first end face of the stub and the first end face of the connector body are polished in the factory, thereby avoiding the need for polishing in the field. The connector and method of the ""688 patent are limited to terminating single optical fibers.
The present invention seeks to overcome the drawbacks noted above by providing a fiber optic connector for ribbon cables that is convenient for use in the field. In one aspect of the invention, a fiber optic cable connector comprises a multi-fiber ferrule extending longitudinally between opposite first and second ends, the ferrule defining at least one longitudinal passageway therethrough, and a plurality of stub fibers disposed in the passageway of the ferrule and secured therein, the stub fibers having ends projecting longitudinally rearward from the second end of the ferrule. The connector also includes first and second opposed splice members each extending longitudinally from a first end proximate the second end of the ferrule to an opposite second end, one of the splice members including longitudinal fiber-aligning grooves and the ends of the stub fibers extending between the opposed splice members in the grooves and terminating at a position intermediate the first and second ends of the splice members. The splice members are configured to allow the fiber optic ribbon to be inserted longitudinally between the second ends of the splice members toward the first ends thereof such that the optical fibers are guided by the grooves into abutment with the ends of the stub fibers that protrude rearwardly from the second end of the ferrule. The connector further comprises a cam movable between an initial position allowing the splice members to move apart to facilitate insertion of the optical fibers therebetween, and a final position in which the cam urges the splice members in the vicinity of the intermediate position thereof toward each other to clamp the optical fibers therebetween.
The stub fibers have mating end faces that are proximate an end face of the ferrule for mating with optical fibers of another connector or other fiber optic device. The mating end faces of the stub fibers preferably are polished in the factory when the ferrule and stub fibers are assembled together. Thus, there is no need to polish any fibers in the field when installing the connector on the end of a ribbon cable, rendering the connector convenient for use in the field.
In one preferred embodiment of the invention, at least one of the splice members has a portion proximate the second end thereof that can flex away from the other splice member to facilitate insertion of the optical fiber ribbon. Preferably, this is accomplished by providing the one splice member with a region of substantially reduced thickness relative to the rest of the splice member, the reduced-thickness region acting as a hinge allowing the flexible portion to pivot relative to the rest of the splice member. The reduced-thickness region of the splice member is spaced from the ends of the stub fibers in the direction of the second end of the splice members. During connector installation, when the stripped ends of the ribbon fibers are inserted between the splice members into the fiber-aligning grooves, the pivotable portion of the one splice member is close to the other splice member to keep the fibers in the grooves and prevent the fibers from crossing over one another. The fiber-aligning grooves can be provided in either the splice member having the flexible portion or in the other splice member. When the thicker ribbon matrix of the cable is inserted between the splice members, the pivotable portion of the one splice member flexes away from the other splice member to allow the cable to be easily inserted. By allowing the end portion of the one splice member to pivot in this manner, bowing of this splice member along its entire length is prevented. Instead, the flexing is isolated to the second end portion, which tends to prevent damage to the cable fibers that otherwise might occur when inserting the fibers into the connector.
The fiber optic connector preferably also includes a flexible ferrule holder surrounding the splice members, and the cam is slidably engaged with the ferrule holder. The cam when slid into the final position compresses one side of the ferrule holder that is proximate one of the splice members so as to urge the one splice member toward the other. The connector preferably also includes a crimp tube surrounding a portion of the ferrule holder that is radially outward of the second end of the splice members, compression of the crimp tube about the ferrule holder causing the splice members to be urged toward each other to clamp the fiber optic ribbon therebetween.
In accordance with another preferred embodiment of the invention, a fiber optic connector for ribbon cable comprises a multi-fiber ferrule and stub fibers as described above, and first and second opposed splice members each extending longitudinally from a first end proximate the end of the ferrule to an opposite second end, the ends of the stub fibers extending between the opposed splice members and terminating at a position intermediate the first and second ends of the splice members. The second splice member proximate the second end thereof has a pivotable portion operable to pivot away from the first splice member to facilitate insertion of the fiber optic ribbon therebetween. The connector also comprises a flexible ferrule holder surrounding the splice members, and a crimp tube surrounding a portion of the ferrule holder that is radially outward of the pivotable portion of the second splice member. Compression of the crimp tube about the ferrule holder causes the portion of the ferrule holder to urge the pivotable portion of the second splice member toward the first splice member to clamp the fiber optic ribbon therebetween.
The connector according to this embodiment of the invention can include the slidable cam described above, and preferably includes fiber-aligning grooves in one of the splice members. The surface of the splice member having the grooves preferably extends axially beyond the second end of the other splice member to facilitate inserting the optical fibers of the ribbon cable into the grooves. Preferably, the second end of at least one of the splice members includes a tapered surface angled away from the other splice member to facilitate inserting the optical fibers between the splice members.
The fiber optic connector of either of the above-described embodiments can also include a housing enclosing the ferrule and ferrule holder, and a coupling surrounding at least a portion of the housing, the housing and coupling serving to adapt the fiber optic connector to a standard interface. Thus, for example, the connector can be made to be compatible with existing MPO multi-fiber connectors or MT-RJ connectors.
The present invention also provides a tool for installing a connector with a slidable cam as described above onto the end of a fiber optic ribbon cable. The tool in accordance with a preferred embodiment of the invention comprises a support base, a connector support cradle mounted on the support base and configured to receive the connector in a position having the central longitudinal axis of the connector extending along a longitudinal axis of the tool, and a fiber-handling fixture mounted on the support base and structured and arranged to engage the fiber optic ribbon to align the ribbon with the connector supported in the cradle such that the optical fibers of the ribbon can be slid axially into the fiber-receiving space between the splice members of the connector. The cradle holds the connector in a fixed position while allowing the cam to slide between the initial and final positions thereof as previously described. The tool also includes a camming carriage slidably mounted on the support base so as to be slidable along the longitudinal axis of the tool, the camming carriage including a cam-engaging member configured to push the cam of the connector from the initial position to the final position when the camming carriage is slid axially toward a rear end of the connector.
Preferably, the fiber-handling fixture also includes a ribbon holder operable to clamp onto the fiber optic ribbon, and guide members defining a guide track within which the ribbon holder is slidably mounted such that the ribbon holder with the fiber optic ribbon clamped therein can be slid parallel to the longitudinal axis of the tool for inserting the ends of the optical fibers between the splice members of the connector.
The fiber-handling fixture preferably also includes a locking device operable to secure the ribbon holder in a fixed position once the optical fibers have been inserted in the fiber-receiving space between the splice members of the connector. This prevents the fibers from moving back away from the stub fibers when the camming carriage is operated to clamp the fibers in the connector.
The tool can also include a magnifying lens movably mounted on the support base for magnifying an operator""s view of the optical fibers and the rear end of the connector to facilitate inserting the optical fibers into the connector.
The invention thus provides a fiber optic connector and installation tool enabling ribbon cables to be easily and conveniently terminated without the need for polishing fibers and without the use of heat-activated epoxy adhesives. The connector and installation tool accordingly are particularly suitable for use in the field. The connector can be made compatible with existing standard interfaces.